Delivery and retrieval of molecules and/or ions of fluids into or through skin tissue is an accepted method for many types of therapeutic and diagnostic treatment, and has led to an increased interest in transdermal drug delivery. Generally, transfer of fluids, particularly those containing macromolecules, through skin tissue is achieved by use of a hypodermic needle. However, use of hypodermic needles can be painful, and provides relatively little control for drug delivery. Also, in the case of treating diseased tissue, the effect of chemical agents on the diseased tissue is often dependent upon delivery of the chemical agent across cell membranes of the cells in the tissue mass, as opposed to simply injecting the chemical agent into the tissue. Further, chemical agents which are injected into diseased tissue typically enter the bloodstream and are transported away from the targeted tissue mass before they have a significant therapeutic effect on the tissue mass into which they were injected. Also, there are many problems that are often associated with treatment of cells by conventional methods, such as by intravenous injection. For example, the cells of melanoma tumors are typically difficult to target by injection techniques because they are in the form of relatively thin tissue. Further, injections can traumatize tissue, thereby possibly spreading potentially malignant growth. In addition, use of some types of intravenous injection, such as those which employ intravenous infusion pumps, can be difficult to control and can promote infection. This complication is especially significant for patients afflicted with immunocompromising illnesses (e.g., leukemias and HIV infection).
One attempt to solve problems presented by transfer of molecules and/or ions across tissues, in particular skin tissue, is employment of a phenomenon called electroporation. Generally, electroporation is a method of temporarily or permanently increasing the permeability of tissue and cell membranes, and of simultaneously providing an electrical driving force. The increased permeability allows transport or migration, of chemical agents through the tissue or across cell membranes into cells. Electroporation has been used to deliver drugs to tissue, in vivo, by applying electrodes to the surface of an organism and applying a voltage between the electrodes which exposes the tissue to an electric field. The tissue becomes electroporated and allows delivery of a chemical agent, such as a drug, which has been applied either topically to the organism or injected into the bloodstream of the organism, across the electroporated tissue and into cells of the electroporated tissue.
The effect of electroporation on tissue can be temporary or long-lasting. Without continued application of an electric field, electroporated tissue often reverts back to its original condition. However, the duration of electroporation is dependent upon the degree of electroporation of the tissue. In other words, to obtain a longer term of electroporation, the term of applied voltage, or the amount of voltage applied, must be increased. Further, use of electroporation has, in some cases, been limited in the amount of ions and molecules that can be transported. This is particularly significant for larger transported species, such as macromolecules.
Therefore, a need exists for a new method for transferring fluids across tissue. In particular, a need exists for a method of modifying skin for transport of a material by electroporation.